High performance microwave and radio frequency integrated circuits are of interest both for military and civilian applications. The ability to design custom integrated circuits and fabricate prototypes in a timely and cost effective manner is a prime concern. Low-power sensor networks have recently become very popular for applications such as logistics and home automations. Remote low-power radio frequency (RF) applications are becoming more prevalent and low power tends to mean short transmission range. This necessitates the need to develop custom RF enhancement chips to meet military and commercial needs that can't be met by commercial off the shelf (COTS) chips.
Low-power radio frequency (RF) transceivers have been used for low-cost, high volume commercial applications that do not always meet the needs of critical military systems. In low-power applications, a tradeoff between transmit range and battery life exists. A simple means of extending transmit range would be to add a custom integrated circuit (IC) between the transceiver and antenna. Using appropriate technologies, a tradeoff in size, efficiency, and performance is achievable.
By way of background, a high electron mobility transistor is referred to as an HEMT. Generally speaking, the two different materials used for the heterojunction in an HEMT must have the same lattice constant. A variation of this is a PHEMT, of pseudomorphic HEMT where an extremely thin layer of one of the materials stretches to fit the other material thin layer. GaAs PHEMTs make very good low noise amplifiers, high efficiency power amplifiers, and have very good RF switch characteristics. The blocks for the RFIC Booster chip take advantage of these high performance characteristics of GaAs to increase the output power, power efficiency, and noise figure.
By way of background, phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). Digital modulation schemes use distinct signals to represent digital data; while Phase-shift keying (PSK) uses phase shifts to represent a unique pattern of binary digits. Generally, each phase is encoded to represent a number of bits. Each pattern of bits represents a symbol that is represented by the particular phase. A demodulator designed specifically for the symbol-set used by the modulator, is used to determine the phase of the received signal and map it back to the original symbol or data. The capability of the receiver to compare the phase of the received signal to a reference signal is referred to as coherent PSK (CPSK). Similarly, instead of bit patterns being used to set the phase of the wave, the phase change can be utilized. The demodulator would then determine the change in the phase of the received signal rather than the phase itself; or the difference between successive phases (also referred to as differential phase-shift keying (DPSK).
In PSK, the chosen constellation points are usually positioned so as to be uniformly spaced around a circle for maximum phase-separation between adjacent points and the best immunity to corruption. Positioning within a circle provides transmission with the same energy and the moduli of the complex numbers they represent will be the same and so will the amplitudes needed for the cosine and sine waves. Two common examples are “binary phase-shift keying” (BPSK) which uses two phases, and “quadrature phase-shift keying” (QPSK) which uses four phases, although any number of phases may be used. Since the data to be conveyed are usually binary, the PSK scheme is usually designed with the number of constellation points being a power of 2.